This invention refers to a material tester and more particularly to a novel and improved electrical system for directing an ultrasonic search unit of an ultrasonic nondestructive material tester, for example, over curved or sloped surfaces and the like.
The use of pulse-echo ultrasonic nondestructive test methods to inspect workpieces for flaws or defects is well-known in the prior art. It has been found that pulse-echo ultrasonic testing is best suited for large workpieces, whereby the search unit must scan the workpiece in such a manner as to ensure that the entire area of the workpiece is inspected. Normally, these scans are made along one axis with indexing of the probe along the other axis before the return scan is started. In the case where curved or contoured workpieces are tested, the workpiece is affixed to a rotatable worktable and an indexing search unit is used.
When testing workpieces by the pulse-echo ultrasonic test method, it is necessary generally to immerse the workpiece and the search unit in a liquid couplant material, such as water, for achieving good ultrasonic coupling.
In the prior art, devices capable of causing motion of the probe system along the scan axes include very complicated electrical tape programmed reading systems and digital and/or analog computers for deriving voltages to change the position of the test probe. The use of such complex systems is quite expensive.
Workpieces having a continuously changing slope are difficult to scan with pulse-echo ultrasonic testing. When testing these workpieces, a simultaneous change in the X and Y axis position is required to test for flaws and defects. Other types of workpieces which are difficult to test are curved wing surfaces of aircraft, turbine blades, and unevenly work railroad rails.
It is desired, therefore, to provide an automatic electrical control system which controls the axis position of a search unit to achieve scanning of irregularly shaped and curved workpieces.